Various printed products, e.g., newspapers, are usually printed according to the rotary offset process. Paper webs are unwound here from rolls and printed on in a plurality of printing couples, partly in multiple colors. The ink to be printed may be metered, e.g., by means of ink screws. The ink register mark indicates the relative positions of various ink layers applied in relation to one another. Even very small deviations of the ink register mark by, e.g., 0.01 mm are perceived by the eye and are found to be disturbing. The register mark deviation provides information on the extent of the position deviations of different ink layers, which together form a printed page of a newspaper. Such register mark deviations may occur along or at right angles to the direction of run of the paper. Deviations at right angles to the direction of run of the paper are usually corrected with the side register, and deviations in the direction of run of the paper web are corrected with the circumferential or ink register.
The ink register mark is affected, e.g., by the distance between the printing mechanisms, the properties of the paper, the water used during the printing, the ink, the roll change, the pull on the paper web or the speed of printing, and ink register controllers are used to correct deviations of the ink register mark.
It is known that marks may be printed on the paper web corresponding to the inks used, and the ink register mark can be determined from the marks printed on. These marks are printed on permanently predetermined areas of the paper web and are shown as an example in FIG. 1. A plurality of marks may be printed in a mark field 1. It is necessary now for the reliable determination of the position of the mark to provide a white area around a mark field 1. If, e.g., marks are placed too close to printed-on areas, it is possible that a sensor will no longer be able to reliably recognize the marks and thus to determine the ink register mark.
Marks and mark fields are defined for each ink register controller product. It can be assumed that the marks are placed during the manufacture of the plates in the predetermined position and in the desired size, and the needed white space was taken into account.
Since mark fields are always arranged at the same site, e.g., laterally at the edge of the plate outside the printing area, handling is simple during the manufacture of the plate. A sensor used to detect the mark fields needs only be set to the predetermined discrete positions in printing mechanisms of different widths in order to reliably detect the mark fields.
If marks are printed at a great distance next to color images, as is shown in FIG. 1, the presetting system calculates no ink removal, e.g., on the basis of the marks placed outside the printing area or, e.g., on the basis of a small mark area for the ink screw zones of the marks. If the printer does not open the ink screws in this case, the marks will not be printed. The controller cannot thus assume its function.
A process for controlling the operations of a printing press, in which coordinates of measuring points are determined for an image recording means from image information that reflects at least the surface of a printed product, the image recording means detecting at each measuring point a measuring field of a defined size on the surface of a printed product, has become known from WO 95/00336 A2.